1. Field of the Invention
This invention relates to electronic circuits and, more particularly, to display processing devices that establish electrical compatibility between a general purpose digital computer memory channel and display equipment.
2. Description of the Prior Art
The industrial revolution was based on the transformation and transmission of energy; the computer is based on the transformation and transmission of information. Mechanical devices developed during the industrial revolution determined the amount and type of physical labor performed by man. Because of the computer's high speed and high precision, it is used to solve many of man's computational problems and thus it is responsible for finding solutions to many of the mental activities that were heretofore performed by man.
Digital computers vary widely in size, speed and type of construction, but practically all digital computers are comprised of the following main parts: one or more devices for entering digital data; a storage or memory unit for temporarily storing the data as it is entered and for storing both the intermediate and final results of the computations; an arithmetic unit for performing the computations; one or more output devices for recording the results of the computations; and a control unit for causing the computer to proceed through the problem by executing the appropriate sequence of arithmetic operations.
The information contained within the digital computer is in the form of electrical signals that are indistinguishable to man without the use of specialized equipment that puts the signals in a form that will be recognized by man. After processing the electrical signals contained within the digital computer, the computer will have a series of electrical signals that represent the answer to some problem. The electrical signals may be transmitted to character and function generators, said character and function generators being coupled to output devices. The character and function generators convert the electrical signals received from the computer to certain analog deflection voltages that are used to drive certain output devices, i.e., cathode ray tubes (CRT), chart recorders, etc. The character generator is used to produce alphanumeric characters and the function generator is used to produce pictorial displays. A display generator (character and function generator) is coupled to one or more display devices (CRTs). As the number of display devices and display generators increases, the number of computer instructions required to produce a specified amount of information on the screen of a CRT increases. Thus, there is an increase in the amount of computer memory that must be used to control the display devices. An increase in the number of display devices also causes an increase in the amount of computer memory that must be devoted to compensate for differences in the rate of flow of information in the computer and in the display generators, and the interval of time required for the computer's direct memory access channel to transmit information to a given display is likewise increased. Therefore, in order to accommodate many display devices, it is necessary to use larger and more expensive computers or many small computers.